Control method for gas burners

ABSTRACT

The invention relates to a control method for gas burners for providing a gas-air mixture. 
     According to the invention, the ionization signal is only used for setting the mixing ratio dependent on the gas quality when the burner flame completely sweeps over the sensor generating the ionization signal. Outside the above-mentioned range, i.e. when the burner flame does not completely sweep over the sensor generating the ionization signal, the gas-air mixture is controlled dependent on the previously determined mixing ratio.

The invention relates to a control method for gas burners using agas-air mixture.

Control methods for gas burners are used for providing a gas-airmixture, i.e. for supplying a gas flow and a combustion air flow to aburner.

In order to ensure an optimum and complete combustion of the fuel, i.e.the gas, within the gas burner, the latter has to be provided with anappropriately balanced gas-air mixture. The ratio between the gas flowand the combustion air flow, and between the gas pressure and thecombustion air pressure, respectively, is referred to as mixing ratio orcomposition ratio.

However, since the quality of the gas provided by the gas supplyvaries—the quality of gas is defined by a so-called Wobbe index—, thegas-air mixture has to be appropriately varied dependent on the qualityof the gas to ensure an optimum and complete combustion.

For making it possible to consider the quality of the provided gas, theprior art discloses control methods according to which an ionizationsignal of a sensor, in particular of a measuring electrode projectinginto the burner flame of the gas burner, is used for adapting thegas-air mixture to different gas qualities. In this respect, it can bereferred to the DE-A-44 33 425, DE 39 37 290 A1, as well as to the DE195 39 568 C1.

In the known control methods for gas burners according to which anionization signal is used, this ionization signal is used over the wholeoperating range of the burner for adapting the gas-air mixture todifferent gas qualities. However, when the operating loads of the burnerare low, the ionization signal strongly depends on external influencesand consequently does not provide any reliable information on thecombustion conditions actually prevailing in the burner. Accordingly,the control methods according to the prior art lead to an instable and,thus, insufficient control.

Starting out from this, the present invention is based on the problem ofproviding an improved control method for gas burners. According to theinvention, the problem is solved by a control method comprising using anionization signal of a sensor for setting a mixing ratio of the gas-airmixture when the burner flame sweeps over the sensor, and setting themixing ratio of the gas-air mixture based on, for example, a previouslydetermined mixing ratio when the burner flame does not sweep over thesensor.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic depiction of a controller assembly according toone illustrative embodiment of the present invention.

Preferred further developments of the invention result from thesubclaims and the description.

The control method for gas burners is used for providing a gas-airmixture for a burner. For this purpose, a gas flow and a combustion airflow are supplied to the burner. The ratio between gas flow andcombustion air flow, and the ratio between gas pressure and combustionair pressure, respectively, is referred to as mixing ratio.

The combustion process in the burner is monitored by means of a sensorgenerating an ionization signal. Information on the combustion processand, thus, on the existing gas quality can be obtained from theionization signal.

An illustration of a burner and controller assembly 10 is shown inFIG. 1. Gas and air flow is provided to a burner 20 that produces aflame 60 when the burner is operating in a first state. A flame 70 isproduced when the burner 20 is operating in a second state. Sensor 30provides an ionization signal to the controller 50. An optical monitor40 may be included to provide a signal to the controller 50, indicatingwhether or not the flame 60 is currently sweeping across the sensor 30.

According to the invention, the ionization signal is used for settingthe mixing ratio dependent on the gas quality exclusively when theburner flame completely sweeps over the sensor generating the ionizationsignal. The underlying idea of this feature according to the inventionis that the ionization signal provides a reliable information on thecombustion process only during this working or operating state of theburner.

Outside the above-mentioned range, i.e. when the burner flame does notcompletely sweep over the sensor generating the ionization signal, thegas-air mixture is controlled dependent on the previously determinedmixing ratio.

The condition whether or not the burner flame completely sweeps over thesensor generating the ionization signal can, for example, be verified byan additional optical flame monitoring means.

1. A control method for providing a gas flow and a combustion air flowin a gas-air mixture to a burner to produce a burner flame, and forusing a sensor that produces an ionization signal to adapt the gas-airmixture to different gas qualities, the method comprising the steps of:optically determining when the burner flame sweeps over the sensor;using the ionization signal of the sensor for setting a mixing ratio ofthe gas-air mixture when the burner flame sweeps over the sensor; andsetting the mixing ratio of the gas-air mixture based on the gas flowand the combustion air flow when the burner flame does not sweep overthe sensor.
 2. A control method according to claim 1 wherein theionization signal of the sensor is used for setting the mixing ratio ofthe gas-air mixture when the burner flame completely sweeps over thesensor, and the mixing ratio of the gas-air mixture is set based on thegas flow and the combustion air flow when the burner flame does notcompletely sweep over the sensor.
 3. A controller for controlling a gasflow and a combustion air flow in a gas-air mixture for a gas burner toproduce a burner flame, the gas burner including a sensor adjacent thegas burner, the controller receiving an ionization signal from thesensor and sets the gas-air mixture based, at least in part, on theionization signal when the burner flame sweeps over the sensor, and setsthe gas-air mixture based on the gas flow and the combustion air flowwhen the burner flame does not sweep over the sensor, the controllerfurther including an optical flame monitor for monitoring when theburner flame does or does not sweep over the sensor.
 4. A control methodaccording to claim 1 wherein the ionization signal of the sensor is usedfor setting the mixing ratio of the gas-air mixture when the burnerflame completely sweeps over the sensor, and said mixing ratio is usedto control the gas-air mixture when the burner flame does not completelysweep over the sensor.
 5. A combustion burner controller that adapts agas-air mixture to different gas qualities, the controller comprising: acombustion burner providing gas and air flow to a burner to produce aflame; a sensor that provides an ionization signal based on thecombustion process in the burner, the sensor positioned adjacent theburner flame such that when the burner is in a first operating state,the flame sweeps completely over the sensor and when the burner is in asecond operating state, the flame does not sweep completely over thesensor; an optical monitor positioned adjacent the flame, the opticalmonitor providing a signal indicating the burner flame is or is notsweeping over the sensor; a controller that sets a gas-air mixture ratiobased on the ionization signal, wherein the gas-air mixture is dependentat least in part on the gas quality; wherein the controller sets thegas-air mixture ratio when the burner is in the first operating state,and uses that gas-air mixture ratio when the burner is in the secondoperating state.
 6. A control method for providing a gas flow and acombustion air flow in a gas-air mixture to a burner to produce a burnerflame, and for using a sensor that produces an ionization signal toadapt the gas-air mixture to different gas qualities, the methodcomprising the steps of: optically determining when the burner flamecompletely sweeps over the sensor; using the ionization signal of thesensor for setting a mixing ratio of the gas-air mixture when the burnerflame completely sweeps over the sensor; and setting the mixing ratio ofthe gas-air mixture based on the gas flow and the combustion air flowwhen the burner flame does not sweep over the sensor.
 7. A controlmethod for providing a gas flow and a combustion air flow in a gas-airmixture to a gas burner to produce a burner flame, the method comprisingthe steps of: optically determining when an operating load of the burneris in a first state and when the operating load is in a second state;accepting an ionization signal from a sensor, wherein the sensor ispositioned in the burner flame when the operating load of the burner isin a first state and at least not completely positioned in the burnerflame when the operating load of the burner is in a second state; using,at least in part, the ionization signal of the sensor for controllingthe gas-air mixture to the burner when the operating load is in thefirst state; and using a measure of the gas flow and combustion air flowfor controlling the gas-air mixture to the burner when the operatingload is in the second state.
 8. A control method according to claim 7wherein, in the first state, the burner flame completely sweeps over thesensor, and in the second state, the burner flame does not completelysweep over the sensor.
 9. A control method according to claim 7 whereinthe determining step determines when the operating load of the burner isin the first state by determining when the burner flame completelysweeps over the sensor.
 10. A control method according to claim 9wherein the determining step determines when the operating load of theburner is in the second state by determining when the burner flame doesnot completely sweep over the sensor.
 11. A method for managing thecombustion of fuel in a gas burner in which a controller controls themixture of gas and air to produce a burner flame, the method comprisingthe steps of: providing an ionization sensor positioned such that whenthe burner is in a first operating state, the burner flame sweeps overthe sensor, and when the burner is in a second operating state, theburner flame does not completely sweep over the sensor; providing anoptical flame monitor coupled to the controller for monitoring when theburner flame does or does not completely sweep over the sensor;providing an ionization signal to the controller when the burner is inthe first operating state; and using the ionization signal to set amixing ratio for a gas-air mixture; wherein when the burner is in thesecond operating state, maintaining the mixing ratio set when the burnerwas in the first operating state.
 12. The method of claim 11, whereinthe ionization signal is only used to set a mixing ratio for a gas-airmixture when the burner is in the first operating state.